This invention relates to a method and apparatus for evaluating a human visual function. More particularly, it pertains to measuring visual acuity, and in a manner particularly advantageous for use with a range of subjects, including infants and young children.
A determination of impaired or other below normal visual acuity is particularly desirable with infants and young children. Early detection can lead to remedial procedures that are often highly effective when begun at an early age. A measurement of visual acuity can provide diagnosis of a condition known as amblyopia, and more commonly termed lazy eye. As indicated, the correction of lazy eye is more successful when commenced at an early age, i.e. during infancy or early childhood.
Prior techniques for measuring visual acuity and hence an amblyopic condition are described in numerous publications, including:
Teller, D. Y., Morse. R., and Regal, D.: Visual Acuity for vertical and diagonal gratings in human infants. Vision Res. 14: 1433-1439, 1974;
Katsumi, O., Oguchi, Y., and Uemura, Y.: Assessment of visual ability in infantile esotropia using the preferential looking method. Jpn. J. Ophthalmol. 25: 457-463, 1981; and
Katsumi, O., Oshima, T., and Uemura, Y.: Development of visual acuity in infant and young children up to three years evaluated with the Preferential Looking method. Ophthalmic Pediatr. Genet. 2: 139-147, 1983.
The evaluation of an amblyopic condition is difficult with subjects who can not speak or indicate a choice, and with those who are not readily tested with complex equipment. It hence is particularly difficult with infants and with young children.
For children over three years of age, it is known that one can evaluate visual function subjectively using the Landoldt letters. However, it is generally not possible to perform such a subjective test, as with the Landoldt letters, with subjects younger than three years of age or the like.
The technique which the present invention employs can, however, be used with such young children, as well as with infants and other humans with verbal communication limitation, including the mentally retarded and the brain damaged.
It is an object of this invention to provide an improved method and apparatus for evaluating a visual acuity function.
It is a further object to provide such a method and apparatus well suited for use with infants and young children and with other humans lacking in verbal communication.
Other objects of the invention are to provide a method and apparatus for measuring a human visual acuity function and further characterized by reliable measurement, low cost, and ease of use.
Other objects of the invention will in part be obvious and will in part appear hereinafter.